docbook2x embeds the current date by default into generated manpages.

Known affected packages

Solution

Set a deterministic timestamp with the --string-param header-3=... parameter.

Example

BUILD_DATE=$(shell dpkg-parsechangelog -S Date | LC_ALL=C date -u "+%d %B %Y" -f -)
...
docbook2x-man --string-param header-3="$(BUILD_DATE)" $input